Existing bridges require substantial maintenance. The maintenance is required at least periodically, if not continuously. For example, it is often necessary to remove the paint (such as a lead-based paint) from the steel structure of a bridge prior to applying a new coating thereto. To remove the paint, conventional sand-blasting or shot-blasting equipment is used. Suitable available measures are taken (as hereinafter discussed) to prevent the debris from falling onto the roadway, or into any water below the bridge, or otherwise polluting the environment.
At the same time, it is also very desirable to facilitate the continuous traffic flow along the roadway, while the maintenance is being performed, and thus avoid a complete shutdown of the traffic flow. While the traffic flow is primarily vehicular or railway traffic, it is also desirable to maintain any pedestrian traffic as well as facilitate access for the maintenance crews. By maintenance, it is understood that any repair or construction on the bridge is contemplated herein.
To maintain the traffic flow while the maintenance is being performed, the prior art has resorted to the use of a shield and containment structure (commonly referred to as a "traffic shield") constructed within or under the bridge, along a given length thereof, and above the deck or roadway of the bridge.
This conventional traffic shield, together with the roadway, provides a complete enclosure for the traffic flow (which may be vehicular, railway, pedestrian or some combination thereof). Within the traffic shield (or thereunder) the traffic is protected against any falling debris--such as paint chips from the bridge, the materials of shot blasting or sand blasting, and any tools, components or structural elements accidentally dropped by the maintenance workers. By the same token, the workers are protected against the vehicular or rail traffic. As a result, a complete shut-down of the bridge is avoided, and the traffic flow is substantially unimpeded while the maintenance is being performed.
However, when the maintenance has been completed on a given length or section of the bridge, the traffic may be halted for a substantial period of time sufficient to enable the workers to completely dismantle the traffic shield, move its individual components to the next successive section of the bridge, and then re-assemble the traffic shield therein. This is time-consuming, hence expensive, and causes a substantial traffic problem; and a need exists for a more efficient solution to this long-standing problem.